This invention relates in general to a floating deck apparatus for placement above the surface of a volatile liquid in a storage tank. In particular, the present invention relates to an improved method of sealing the annular space between the floating deck edge and the interior of the storage tank walls by providing for multiple wiper assemblies to limit evaporation of the volatile liquid.
Floating decks, which may include internal floating covers, internal floating pans or external floating roofs, have become the main means of preventing evaporation losses from storage tanks containing volatile liquids such as petroleum and petroleum distillates. Such decks help to form a seal within the storage tank and the decks rise and fall with the volatile liquid level within the tank to further prevent excessive evaporation losses. A means for improving the annular seal between the edge surfaces of such floating decks and the interior wall surfaces of the storage tanks is desperately needed with today's shortages of petroleum products throughout the manufacturing world.
There have been many attempts to provide such an annular seal for floating decks. Such seals tend to fit into four classifications, namely a solid flexible wiper, a fabric encased foam, a liquid filled plastic envelope or a plastic log. Such seals suffer from the disadvantage of not fully sealing the annular space between the folating deck and the interior of the storage tank from volatile liquid evaporation. In particular, since storage tanks cannot be made either perfectly round or with perfectly smooth interior wall surfaces, sealing assemblies of the prior art have become subjected to loss of sealing as the sealing arrangements pass over irregularities in the storage tank inner wall surfaces. Such loss of sealing may be the result of the former sealing arrangements passing over and being forced inward by such obstructions as rivet heads, weld seams or lap joints utilized in the actual formation of the storage tank walls.
Accordingly, it is a principal object of the present invention to provide an improved sealing arrangement for storage tank floating decks.
A further object of the present invention is to provide a sealing arrangement for the peripheral edge of such a deck as outlined above which minimizes evaporative losses from the storage tank.
It is an additional object of the present invention to provide a multiple peripheral seal for floating decks which is capable of overcoming irregularities in the inner wall surfaces of such a storage tank as outlined above in order to further minimize evaporative losses from such a tank.
Further objects and advantages of the present invention will become apparent from a consideration of the following specification.